Process for the reduction of iron oxide



Feb. 15, 1966 Filed April 2,

PROCESS FOR THE REDUCTION OF J. E- K. MEYER ETAL IRON OXIDE BALL/N6 GREEN PELLETS HEA MG F/ 7 INDURATE+D PELLE rs CARBON- REDUCTION -L/ME5TONE OR DOLOM/TE CHAR COOLING SEPARATION 4 SEPARATION IRON-IRON ox/DE NON- METALL/CS HYDRATED LIME OR DOLOM/ TE 90- E Q k) 80 i v E B CONVENTIONAL F/ G. 4 J: 7o w PROCESS Q 3 5 Lu 5o E E PRESENT LL 5 1 so wmrss D D 6 k 8 E 40 2 D Q a: D 2 1: u E g Q: 20. r-

CHARGE DIRECTION OF DISCHARGE END BURDEN /N K/LN END INVENTORS.

JUL/US E. K. MEYER BYJA ROSLAW G. SIBA KIN AGENT Feb. 15, 1966 J. E. K. MEYER ETAL 3,235,375

PROCESS FOR THE REDUCTION OF IRON OXIDE Filed April 2, 1964 3 Sheets-Sheet 2 IN VEN TORS JULIUS E. K MES El? BY JAROSLAW c; .S/BAK/Al AGENT Feb. 15, 1966 J. E. K. MEYER ETAL 3,235,375

PROCESS FOR THE REDUCTION OF IRON OXIDE 3 Sheets-Sheet 5 Filed April 2, 1964 W Mm K 0 MA T B N n S T w M u N .G I A E 9 S um Wm J] a Y B 2361 I? 58 $38 s$o$ Q5 SE28 mmmqw wkm s United States Patent 3,235,375 PROCESS FOR THE REDUCTION OF IRON OXIDE Julius Emil Kurt Meyer, Frankfurt am Main, Germany,

and Jaroslaw George Sibakin, Ancaster, Ontario, Canada, assignors to The Steel Company of Canada, Limited, Hamilton, Ontario, Canada, a company of Canada Filed Apr. 2, 1964, Ser. No. 356,734 22 Claims. (Cl. 7534) This is a continuation-in-part of Serial No. 103,356, filed April 17, 1961, and now abandoned.

This invention relates to an improved process for the reduction of iron oxide to a lower state of oxidation at a temperature below the melting temperature of iron. It is particularly directed to the production of a product in which from about 60% to about 100% of iron present is in the metallic state.

Processes have become known for reducing iron oxide to metallic iron with a reducing agent at a temperature below the melting temperature of metallic iron and, usually, below the melting point of ferrous oxide. These processes involve reactions which can be expressed by the equations:

1. 3Fe O +CO 2F6304+CO2 2. 3. FeO-l-COSFe-f-CO 4. CO2+CS2CO These reactions are well know. However, economic and operating problems have been encountered in their application, particularly when the iron oxide is reduced in the solid state. For example, a rotating kiln type reactor in which iron oxide ore, solid carbonaceous reducing agent and a scavenger are fed into one end and solid reaction products are discharged from the other end would appear, superficially, the most logical type of apparatus to employ from the points of view of simplicity and capital and operating costs. Difficulties have been encountered, however, in the operation of the rotary kiln which have adversely effected its use in the reduction of iron oxide as a practical, economic, commercial scale operation. These difiiculties include the adhesion of particles of the charge to the wall of the reactor, thus restricting the capacity of the reactor and the free flow of charge mixture and reaction product therethrough, and the agglomeration of particles of the charge which prevents free access of carbon monoxide to the iron oxide particles, thereby impeding the rate and efiiciency of the reaction.

A further difliculty may be encountered due to the fact that Reactions 2, 3 and 4 are reversible and the direction which the reactions take and the rate at which they proceed depend on temperature and, in respect of Reactions 2 and 3, on the partial pressure of carbon monoxide which, in order to obtain a satisfactory reaction rate, should be substantially higher than the partial pressure of carbon dioxide. Reaction 4 is primarily dependent on temperature and thus, in order to maintain a maximum partial pressure of carbon monoxide for rapid and efficient reduction of iron oxides to metallic iron on an economically practical basis, it is essential to maintain a high and substantially uniform temperature throughout the reaction zone. Due to the relatively slow rate of decomposition of carbon monoxide according to Reaction 4 and to the short residence time of the gases in the kiln in a countercurrent process, non-stable mixtures of gases, richer in carbon monoxide than is required by the equilibrium conditions, may exist at temperatures lower than those in the reaction zone. This increases the possibility of the reactions of reduction, particularly Reactions 1 and 2, taking place at 3,235,375 Patented Feb. 15, 1966 the very beginning of the reaction zone or even in the heating zone. A sufliciently high and substantially uniform temperature in the reaction zone, however, has a decisive influence upon the rate of the reactions of reduction.

In contrast with the known processes having the above inherent disadvantages is the process described and claimed in United States Patent 3,029,141. In general, this patent teaches that iron oxide can be reduced in the solid state to a lower state of oxidation up to and including metallic iron by employing iron oxide, solid reducing agent and dolomite and/ or limestone particles within predetermined size ranges and conducting the reducing reaction under closely controlled, substantially uniform temperature conditions.

Close control of temperature is obtained by supplying fuel from an external source at spaced intervals along the length of the kiln supplementary to the solid reducing agent, a solid carbonaceous material, to provide at least part of the total amount of the heat required to maintain the reduction zone at reaction temperature, and a free oxygen containing gas at spaced intervals along the length of the kiln in amount sufficient to provide oxygen for reaction with carbon contained in said solid carbonaceous matter to form carbon monoxide.

Although the process disclosed in United States Patent No. 3,029,141 overcomes many of the problems of the prior art, we have discovered certain improvements in the operation of this process. We have found that the introduction of a free oxygen containing gas in amount sufficient to provide oxygen for substantially complete reaction with the combustible components of an increased amount of liquid or gaseous supplementary fuel which is required for supplying process heat and a portion of the process reducing gases, together with oxygen available for reaction with about 20% to about of the carbon contained in the solid carbonaceous matter charged, provides improvements. Not only is the requirement for solid carbonaceous matter reduced but, also, the thermal efiiciency of the process is further enhanced and a considerably improved temperature profile control and optimum production of reducing gases are obtained.

Although it will be understood that this process is free of hypothetical considerations, it is believed that the addition of a free oxygen containing gas in amount sufficient to ensure, inter alia, substantially complete combustion of the supplemental fuel introduced at spaced intervals, such as, for example, natural gas, results in the following reactions:

5. onnm+ O ,nCO +g H O The carbon dioxide and water vapor produced by this reaction proceed to react, in part, with the solid carbonaceous matter in the charge as follows:

7. O +2CS2CO results in the following reduction reactions:

The reduction operation according to the above reactions proceeds at an accelerated rate, provides improved recovery and output of the partially reduced roasted or green iron oxide pellets with enhanced economics in the consumption of fuel, and permits maximum uniform reaction temperatures heretofore thought not feasible without undue hazard and agglomeration of the charge.

Also, the process taught in the United States Patent No. 3,029,141 teaches that supplemental fuel and/or oxygen supplied to the kiln at spaced intervals are introduced radially into the kiln thus impinging, under certain circumstances, on the diametrically opposed portion of the kiln wall or on the surface of the charge. It has been found, when practising the process, particularly under industrial conditions, that localized over-heating of the kiln wall can occur resulting in the formation of accretions which impede the throughput of the charge while occupying valuable kiln space.

It has been discovered that the introduction of supplemental fuel and a free oxygen containing gas in a direction parallel to the long axis of the kiln countercurrent or concurrent to the main flow of gases in the space between the surface of the bed of charge mixture and the opposing wall of the kiln results in an improved heat distribution and a more effective production of carbon monoxide gas while obviating localized over-heating of the charge mixture and formation of wall accretions.

The present invention is a process for improving reduction proceses of the type disclosed in United States Patent No. 3,029,141.

It is therefore a principal object of this invention to provide such an improved process. An important object is to improve the thermal efficiency of the process and enhance the formation of reducing gases so as to minimize the requirement for solid carbonaceous matter in the charge mixture and thereby maximize the iron oxide throughput. Another object is to provide improved temperature control throughout the heating and reaction zones permitting an increased mean temperature in the reduction zone thereby effectively accelerating the rate of the reduction. A still further object of this invention is the provision of a process which will permit reduction of green or unheated iron oxide pellets without the need for an intermediary heat-hardening step.

These various objects have been met in a completely effective manner. In general, the process of this invention follows the process of United States Patent No. 3,029,141. The improvement resides in the discovery that an increase in the quantity of supplemental fuel added at spaced intervals along the length of the kiln to from about to about 50% of the total fuel energy required for the solid reduction process together with an increased amount of free oxygen containing gas at spaced intervals along the length of the kiln to permit substantially complete combustion of all the supplemental fuel and a portion only of the solid carbonaceous material permits a decrease in the quantity of solid carbonaceous material in the charge to an amount which supplies from about 50% to about 90% of the total fuel energy required for the solid reduction process, and which permits the discharge of carbon with the reacted charge mixture, resulting in unexpectedly improved operation of the process. The decreased load of solid carbonaceous material permits increased throughput of the iron oxide ore and rapid attainment of the desired reaction temperature, thereby increasing the length of the effective reduction zone in the kiln with notable improvement in utilization of available kiln volume. We have found that the introduction of solid carbonaceous material in the charge in amount substantially below 150% of that theoretically required for complete reduction provides about 92% to about 97% reduction of the iron values in the ore.

Prior to a more detailed description of the invention, a general description of the steps of the process is set out hereinbelow. The improved process for the complete or partial reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone comprises, in general, the steps of: feeding into the heating zone of the kiln a mixture of hard burned or green iron oxide pellets of a particle size within the range of from about 3 mm. to about 15 mm., solid carbonaceous material of a particle size of from about 0.15 mm. to about 12 mm., and a flux in which the major portion is of a particle size larger than about 0.5 mm., the carbonaceous material being supplied in an amount which provides from about to about 90%, preferably about to about 80%, of the total fuel energy required for reduction the iron content of the charge and for maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture; reacting the charge mixture in the reduction zone at a temperature within the range of from about 650 C. to about 1200 C., preferably about 1150 C., but below the agglomerating temperature of the charge mixture; maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length, combustible material which provides from about 10% to about 50%, preferably from about 20% to about 40% of the total fuel energy required for reduction of the iron content of the charge and for maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture; adding a free oxygen containing gas at spaced intervals along its length in amount sufficient to provide oxygen for reaction with the supplemental fuel and a portion of the solid carbonaceous material to supply the necessary heat and reducing gases.

The process is described in detail hereinafter with reference to the accompanying drawings in which:

FIGURE 1 is a flow sheet of a preferred embodiment of the process;

FIGURE 2 is a side elevation partly in section and partly schematic of a rotary kiln-type reactor and cooler assembly suitable for carrying out the process;

FIGURE 3 is a schematic view of a reactor in which carbon separated from the reaction mixture discharged from the discharge end of the reactor is returned to the reaction and with solid carbonaceous material is fed into the reactor with the iron oxide pellets and scavenger; and

FIGURE 4 is a graph which illustrates the percent of the charge volume occupied by the solid carbonaceous: material during the operation of conventional processes and the process of this invention.

Like reference characters refer to like parts through-- out the description and drawing.

The iron oxide treated by the process of this invention preferably, but not necessarily, is in the form of a high grade iron ore or an ore which may have been beneficiated by known processes to reduce gangue material, and may have, for example, of the order of from 60% to iron content. Impurities other than oxidizable impurities, such as sulphur, are not eliminated during the operation of this process. Sulphur may be eliminated by' preliminary volatization, roasting, sintering and/ or by the reduction process of the present invention. The desulphurization of green pellets by the present process is an additional advantage not heretofore possible by known direct reduction techniques.

Referring to the flow sheet illustrated in FIGURE 1 of the drawing, the iron ore particles are formed into pellets or nodules of a desired shape in agglomerating step 1. This step may be omitted if the ore, as received, is in the form of lumps of suitable size and composition. The machine employed for this agglomerating step is a conventional pelletizing machine in which particles of ore,

are agglomerated into a desired size and shape. Conventional machines are available for this purpose, such as rotating granulating drums and pelletizing discs. We have found, having regard to the desired rate of the reducing reaction and the extent of the reduction which can be obtained in an economically practical time period, that the iron ore, as received or as agglomerated into a desired shape, should be at least about 3 mm., and preferably from about 6 mm. to about 15 mm. in size. That is, if the pellets are spherical, they should be at least about 3 mm. in diameter. If they are of any other shape, such as elliptical, polyangular o-r rod-like, the minimum dimension should be at least about 3 mm. The above sizes and shapes have been found to give optimum surface to volume ratios to reduce the danger of sticking and to minimize the surface area exposed to contamination by sulphur from the solid carbonaceous material used in the reducing reaction and, also, to minimize the formation of an adhering film of flux or scavenger, ash oxides and solid fuel fines. For satisfactory reduction within a reasonable time period, the maximum size is about 15 mm.

The products from agglomerating step 1 may be, if desired, passed to heating step 2 wherein they are heated at a temperature sufficient to cause the iron oxide particles to bond together as a hard, coherent body. Having regard to the nature of the gangue material associated with the iron oxide, this temperature usually is within the range of from about 1,000 C. to 1,500 C. Optimum temperature conditions can be readily determined for specific ores or concentrates. Preferably, the heating step is conducted in the presence of a free oxygen containing gas, such as air, oxygen enriched air or oxygen. This step, which can be conducted in a conventional shaft furnace or on a moving conveyor, such as a sintering machine, serves several useful purposes. The iron oxide particles are bonded together into strong, coherent bodies which are resistant to disintegration in subsequent steps of the process and the sulphur content of the ore can be substantially eliminated.

We have found that green pellets, because of their structure and high porosity and permeability, can be substantially desulphurized. The agglomerating step preferably is performed immediately prior to [the introduction of the green pellets into the reducing kiln with solid carbonaceous material and a scavenger such as dolomite.

The pellets, indurated or green, are introduced to the kiln with solid carbonaceous material and a fiux or scavenger. The flux or scavenger, such as limestone, CaCO or, preferably, dolomite (Ca,Mg)CO is provided in the reaction mixture primarily to combine with the sulphur content of the solid carbonaceous material and the iron oxide pellets as calcium and/or maguesium-sulphur compounds such as, for example, calcium sulphide, and thus prevent the sulphur from combining with reduced iron as iron sulphide. Dolomite is preferred as a fluxing agent as it can be readily crushed to particles of a desired size which have less tendency to spall or disintegrate during passage through the kiln. Also, the use of a scavenger such as limestone or dolomite minimizes agglomeration of the charge particles during travel through the reducing zone. We have found that the sizes of the particles of solid carbonaceous material and limestone or dolomite are important to the successful operation of the reduction step, particularly when it is conducted in a rotating, kiln-type reactor or other type furnace wherein the materials which form the charge mixture are tumbled and rolled continuously together.

The particles of solid carbonaceous material, whether in the form of coal, coke or the like, should be smaller than 12 mm, for indurated pellets and smaller than 6 mm. for green pellets. A size range of carbonaceous particles of 12 mm. to 1 mm. has been found satisfactory for the indurated pellets and a size range of 6 mm. to 0.15 mm. been found satisfactory for green pellets. For the processing of green pellets, the use of solid carbonaceous material in the above size range results in the production of a uniformly sized and coherent reduced product with a minimum of degradation of the pellets and a more rapid and efficient reduction; thereby improving the economies of the process. There is no critical minimum size for the solid carbonaceous particles, but to minimize dust losses and for convenience in handling, particles greater than about 0.15 mm. in size are preferred.

The particles of limestone or dolomite should be in the size range of from about 0.5 mm, to about 3 mm. The presence of scavenger fines creates an operational difficulty in that at the temperature at which the reaction is conducted they tend to adhere to the lining of the kiln and to the exposed surfaces of the pellets. The limestone or dolomite should be provided in the charge mixture in an amount at least about 3%, by weight, of the charged pellets dependent upon the sulphur content and size of the iron oxide pellets and sulphur content of the carbonaceous material to ensure the presence of an excess of reactive surface to scavenge the sulphur contained in the reactants.

An important feature of this process is the reduction in the amount of solid, carbonaceous material consumed in the reactor. Heretofore, it has been believed necessary, as taught for example in United States Patent No. 2,829,042, issued April 1, 1958, to provide carbon in the solid carbonaceous material in large excess, for example, five times the theoretical amount required for complete reduction of the iron oxide to metallic iron in achieving only to reduction. This quantity was required to ensure the presence of a large excess of carbon throughout the entire reactor to meet the requirements for carbon and carbon monoxide as reducing agent and as a source of heat. In addition to occupying otherwise useful space in the reactor, and thus reducing its capacity for its intended purpose, the large excess of solid carbonaceous material must be separated from the discharged reaction mixture and recycled to the kiln. About 10% of the carbonaceous matter re-cycled usually is lost in this latter operation, which adds to the overall cost. Also,

this conventional procedure has the added important disadvantage in that it is not possible to obtain with rapidity the desired reaction temperature, thus limiting the effective length of kiln available for reduction of iron oxides.

We have found that these operating difiiculties can be overcome by supplying carbonaceous material in an amount which provides from about 50% to about 90%, preferably from about 60% to about 80%, of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the solid reaction products, and thereafter providing fuel at spaced intervals from an external source to provide supplemental requirements. We have found that supplemental fuel which supplies from about 10% to about 50%, and preferably from about 20% to about 40%, of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture, should be provided from an external source at spaced intervals along the length of the kiln to obtain optimum results in the operation of the process of this invention. This supplemental fuel can be provided in the form of particulated solid, liquid or gaseous hydrocarbons such as powdered coal, natural gas or oil which is directed into the reactor parallel to the long axis thereof and concurrent and/ or counter-current to the flow of charge mixture, i.e. in counter-current and/ or concurrent to the flow of reducing gases.

The quantity of solid carbonaceous material introduced into the kiln preferably should be provided in an amount sufiicient to have in the discharge of the kiln 0.15 pound of carbon per pound of indurated iron oxide pellets charged, for high level reduction such as 95% reduction,

and lesser amounts of solid reductant, such as 0.05 pound of carbon per pound of iron oxide pellets charged, for lower levels of reduction such as 60% reduction.

As a specific illustration of the improved operation of the present process, we have found that the presence in the charge mixture of 1.29 (129%) of the theoretical amount of carbon required for complete reduction of iron oxide to metallic state provides a 95.3% reduction of iron oxide pellets containing 66% iron.

The carbon monoxide content is maintained at a strongly reducing level throughout the reduction zone and it does not fluctuate even under a rapid change of operating conditions. Accordingly, it is not necessary to have available a large excess of carbon in the charge to the kiln to compensate for such fluctuations.

FIGURE 4 illustrates the relative charge volume occupied by solid carbonaceous material in the operation of conventional reduction processes compared to the reduction process of the present invention. The solid carbonaceous material required in conventional processes occupies about 68% of the volume of the charge in the reactor as compared with about 51% of the volume of the charge in the reactor when part of the fuel is supplied with the charge mixture and part at spaced intervals along the length of the reduction zone according to the present process.

Solid carbonaceous matter introduced with the pellets through the feed end of the kiln preferably should be of a type which is non-caking, or non-agglomerating, at the temperature which prevails in that portion of the kiln. The introduction of high volatile non-agglomerating coals, such as lignites, into the feed end of the kiln may not be entirely satisfactory since a substantial part of the chemical energy contained in the volatile matter of the coal will not be utilized inside the kiln because of losses with exhaust gases. The low volatile non-agglomerating coals, such as, for example, anthracite or semi-anthracite preferably are fed with the original charge. The latter coals usually are more expensive than high-volatile fuels such as bituminous and sub-bituminous coals, lignites and the like and it is one of the features of this invention that only a relatively small part of the carbon required as fuel and reductant in the kiln which is introduced with the pellets need be of the relatively low volatile non-caking type and the carbonaceous matter which may be supplied directly into the reduction zone by late charging can be of a high er volatile type. The volatile matter resulting from the distillation of the coal in the reduction zone is consumed in the kiln and the heat utilized by the process. The excess carbon discharged from the kiln can be re-cycled and introduced into the kiln with the charge and serve as all or a portion of the low volatile carbonaceous material of the charge, as shown in FIGURE 3. The re-cycled fuel or carbon does not contain volatile matter in any appreciable amount and is non-agglomerating in character.

When high volatile coal is used, the kiln, of course, is still provided with radial burners as shown in FIGURE 2 and is similar to the kiln operating on a non-agglomerating carbonaceous material and gaseous fuel. The high volatile coal is late charged and subsequently reintroduced with the charge after recovery from the kiln discharge. Thus, the process, as shown in FIGURE 3, illustrates the possibility of using various solid fuels and reductants in the operation of the process.

Another important feature of this process is the provision of a free oxygen bearing gas such as air at spaced intervals along the length of the kiln in amount sufficient to provide oxygen which will react with substantially all the supplementary fuel according to the reactions above, namely Reaction 5 for natural gas and Reaction 7 for a carbonaceous material. Sufficient oxygen is also added to react with at least about 20% and not more than about 75% of the solid carbonaceous matter added in the charge according to Reaction 7 for the production of carbon monoxide which will react with the iron oxide according to Reactions 1 through 4 and Reactions 8 and 9.

The free oxygen bearing gas is introduced under a positive pressure to accurately control the quantity of oxygen added and thus permit the necessary degree of combustion within the kiln for the desired temperature profile.

The quantity of free oxygen containing gas introduced to the kiln at spaced intervals is controlled to ensure a strongly reducing atmosphere at the discharge end of the kiln. Sufficient oxygen is desired at the heating zone of the charge end of the kiln to ensure substantially complete combustion of the exhaust gases.

The charge mixture fed into the feed end of the reactor is heated to reaction temperature in the heating zone and advances towards and through the reduction zone wherein Reactions 1, 2, 3, 8 and 9 above, proceed to the desired extent. While the process can be operated to reduce about 100% of the iron content of the pellets to metallic state, it usually will be conducted in view of economic considerations, to obtain a reduction of from about to about 98% of the iron content, leaving some of the iron in the form of an iron oxide. Such a product is found to be suitable as feed for iron and steel making furnaces. It will be understood, however, that the degree of reduction can be closely controlled and it may be desired to obtain a reduction less than within the range of from about 60% to about 95%, for iron making. The process is very flexible and the conditions of temperature and reaction time can be determined readily for the treatment of a specific iron oxide ore to obtain the desired reduction having regard to economic factors and the requirements of the iron and steel furnace in which the nroduct is to be used as feed material.

The temperature at which the reducing reaction is conducted is important in the operation of the process. As stated above, it is preferred to heat the incoming charge as quickly as possible to reaction temperature and it is essential that a substantially uniform temperature should be maintained throughout the reduction zone of the reactor and that this temperature should be maintained within narrow limits to obtain desired reduction within the shortest possible period of time.

The maximum temperature which can be employed in the reducing reaction is determined primarily by the nature and the amount of the gangue materials associated with the iron oxide in the pellets. The softening temperature of a specific iron ore, or a mixture of iron ores, can be readily determined by conventional tests. The maximum temperature can then be determined at which the reaction can be conducted without fusion or incipient fusion at surfaces of the pellets, the particles of solid carbonaceous material and flux which would favour the adherence of charge particles to the wall of the reactor; the formation of an adhering film on the surfaces of the pellets; or of the agglomeration of particles of the charge.

We have found that the supplemental fuel and a free oxygen bearing gas must be introduced at spaced intervals in the kiln in a direction substantially parallel to the longitudinal axis of the kiln in order to obtain the high thermal efiiciency of the process together with desired control of the temperature range within the heating and reduction zone without either localized overheating of the kiln wall or charge and resulting aggregation or localized zones of oxidation. The gases introduced preferably are directed countercurrent to the general flow of reducing gases within the reduction zone to effect substantially complete combustion and conversion to reducing gases before contact is made with the iron oxide in the charge. It may be preferred to divide the flow of supplemental fuel and/or free oxygen bearing gas such that a portion is directed countercurrent to the general flow of reducing gases and the remainder concurrent with the flow of reducing gases.

FIGURE 2 illustrates, partly schematically and partly in section, an elongated rotary kiln-type reactor in which the above described step 3 of the process can be conducted. Charge mixture comprised of iron oxide pellets, solid carbonaceous material and flux is fed from a source of supply, such as a transfer chute 10, through a feed chute 11 to the feed end 12 of the kiln. A vibrating tray feeder may be preferred for feeding green pellets to minimize crushing and size reduction of the pellets.

The kiln is of circular section. It is formed of an outer steel shell 13 and an inner lining of refractory material 14, such as fire clay, magnesite, chrome or the like. The kiln is supported on trunnions 15, according to conventional practice, and is adapted to be rotated at a predetermined number of revolutions per minute or per hour, such as by a motor 16 through a train of speed reducing gears 17, the final one of which is meshed with a gear 18 secured around the shell 13. It can be mounted in a horizontal plane with vanes, not shown, for advancing the charge from the feed end to the discharge end, or it can be mounted at an angle of, for example, from 2 to 4 to the horizontal, as illustrated, to cause the charge mixture to flow by gravity from the feed end to the discharge end.

Upstanding baflles or retention rings 19 may be provided, if desired, at spaced intervals along the kiln and extend a short distance thereinto to retard the rate of flow of pellets through the furnace to ensure that they are retained in the heating and reduction zones the required residence periods and to increase the equivalent bed depth.

The charge mixture fed into the kiln advances to and through the heating zone 20 wherein it is heated to reaction temperature by the heat of the gas flowing countercurrent thereto, by the provision of heat generated from the combustion of fuel supplied from an external source and by the heat generated in the bed by oxidation of carbon.

The charge heated to reaction temperature is advanced to the reduction zone 21 which is maintained at reaction temperature in part by heat generated from solid carbonaceous material fed into the kiln with the iron oxide pellets and in part by the combustion of heating fuel su-pplied to the kiln at spaced intervals along its length by burners 22 and an axial burner 23 at the discharge end. The burners 22 extend into the kiln beyond the bed of charge mixture to discharge the fuel into the space between the surface of the bed of charge mixture and the opposing Wall of the kiln. The burners terminate in nozzles 24 which are positioned parallel to the long axis of the kiln and are directed towards the discharge end so that the fuel is discharged into the kiln in a direction concurrent to the flow of the charge mixture and countercurrent to the flow of the gases, or are divided and directed towards the discharge and charge ends of the furnace as illustrated by burner nozzle 25 so that the fuel is discharged in both directions. The burner nozzles 24 and 25 described in detail in co-pending application No. 289,671 are connected to a valved fuel supply manifold 26 by lines 27.

Air necessary for the combustion of fuel and for the reactions which take place in the kiln is supplied under pressure through burners 22 via air supply line 29 having compressor 28 and through axial burner 23 via air supply line 30 having compressor 39. The air and supplemental fuel supplied to each of burners 22 and 23 preferably are maintained separate until fed into the kiln and each burner can be controlled within very narrow limits to supply from zero to maximum air and from zero to maximum fuel at each supply point along the length of the kiln. The supply of supplemental fuel and air to each burner 22 can be manually controlled or automatically controlled by thermocouples 32 opposite each burner, thermocouples 32a adjacent each burner, and by exhaust gas analyser 33. It will be understood that although each burner can be regulated to introduce from zero to maximum supplemental fuel and air, the total quantity of said fuel and air introduced along the length of the kiln will be within the limits of operation described in detail hereinabove. The gases fed into and formed in the kiln preferably should flow countercurrent with the solids as illustrated most clearly in FIGURE 3. Provision is made to pass exhaust gas out of the feed end 12 by exhaust stack 34. The exhaust gas can be discharged to the atmosphere or, if desired, it can be collected for the recovery of any solid, gaseous or heat values contained therein.

The reaction mixtures comprised of reduced iron-iron oxide pellets, ash oxides, unreacted carbon particles and reacted and unreacted scavenger or flux particles, is dis charged from the discharge end 35 of the kiln. It is usually necessary to cool the reaction mixture, step 4 of FIGURE 1, to a temperature at which it can be handled conveniently by conventional equipment for the recovery of the desired iron-iron oxide pellets. Cooling should be effected under conditions which prevent re-oxidation of the pellets. A convenient procedure is illustrated in FIGURE 2 whereby a strongly reducing atmosphere is maintained at the discharge end of the kiln. The reaction mixture is passed, in this reducing atmosphere, to a cooler 37 wherein it is cooled, in a neutral or reducing atmosphere, to about atmospheric temperature, or at least to a temperature at which the pellets can be separated from the reaction mixture without danger of re-oxidation. The cooler 37 can be of a conventional type, such as a rotating kiln externally cooled by a water spray from water line 38. A reducing atmosphere is maintained in the cooler 37 by maintaining transfer chute 39 at a positive pressure.

The iron-iron oxide pellets can be separated from the reaction mixture discharged from the cooler 37 by screening or by a conventional separation process indicated in FIGURE 1 by step 5. The recovered pellets are either passed directly to an iron or steel making furnace or they can be passed to storage. It may be desirable to coat the pellets with a protective film, such as graphite or lime, or both, or by other means which protect them from oxidation. A protective coating of carbon on the reduced pellets can be obtained in the cooling step by the deposition of soot according to Reaction 4. The pellets or metallic fines which may have originated from some degradation of pellets during reduction can be briquetted should a high density metallic product be desirable. The nonmetallics from step 5 are screened in step 6 to recover the char which is re-cycled to the ore charge or latecharged to the kiln.

The temperature at which the reduction zone is maintained depends on the nature of the iron ore and the gangue material associated with it. The maximum reduction temperature can be determined readily by conventional tests having regard to the fact that it is desired to inhibit the formation of a film or gangue material on the surfaces of the pellets and the sticking of particles of the charge on the wall of the kiln. In the treatment of the particular ore in the Examples set out hereinafter, the

reduction zone was maintained at a temperature within the range of from 920 C. to 1130 C. but we have found for certain ores that a temperature of 1200 C. is permissible.

The following example illustrates results obtained in the operation of the process. The kiln employed was 30 feet long, 1.5 feet inside diameter and was rotated at /3 revolution per minute. The cooler was 20 feet long, 1 foot inside diameter and was rotated at speeds about revolution per minute.

The iron oxide concentrate was pelletized and the pellets heated in an oxidizing atmosphere on a travelling grate prior to introduction to the reduction kiln. The feed rate to the reduction kiln was maintained so as to result in a degree of filling of about 20% of the kiln capacity with a total residence time in the kiln of about 1 /2 hours of which about 2 /2 hours were spent in passing through the reduction zone. Approximate analyses of the pellets used is shown in Table 1.

Anthracite coal with 86.3% fixed carbon and 1% S and coke with 82% fixed carbon and 1.2% S were used. The supplemental heat supplied through the axial and radial burners was coke oven gas.

The various conditions of operation were as follows:

Solid reductantcokeparticle size minus 1 mm.

Anthraciteparticle size to 1 mm., 0 to 3 mm., 0 to 5 mm., 0 to Pellets-particle size minus 3 mm., 6 to 10 mm., 10 to mm., to mm., 25 to 35 mm. Limestone particle size (Tyler minus 1 mm., 1 to standard screen). 3 mm. Dolomite-particle size plus 1 to 3 mm., plus 1 to 6 mm., plus 1 to 10 Amounts used0%, 4%, 6%, 8%, 12% by weight of the pellets charged.

Temperature in the reduction zonebetween 900 to 1130" C. depending on the type of pellets used. Various amounts of anthracite and coke were used during the trials.

The tests were conducted with different combinations of particle sizes, charge components, amounts of additives in the charge and temperatures. The conditions of each test were maintained substantially constant throughout the test, for example, for 12 hours. The test periods were part of a continuous trial campaign which lasted from 5 to 6 days. The experiments were conducted for several campaigns. Purified coke oven gas was used, when necessary, and supplemental heat supplied by burners 22 and 23 The charge input rate, the discharge rate, the volume of gas and air, as well as the volume and composition of the waste gases, were measured on a continuous basis. The temperature profile of the kiln was continuously measured and maintained within preselected limits. The amount and particle size distribution of the soild discharge of the kiln were measured and its chemical composition analyzed.

It was found that the most satisfactory reduced pellets produced in these tests contained up to 96% of the iron in the metallic state. They had a sulphur content below about 0.03% and were free from adhering flux and fly ash. They were in an ideal condition for charging into an iron or steel making furnace. The most satisfactory reduced pellets were obtained when the iron oxide pellets were from about 3 to about 15 mm. in size. At least 4% flux by weight of the ore charged of a particle size of from about 1 mm. to about 6 mm. was suflicient to maintain the sulphur in the reduced pellets below 0.03%; at least 6% flux by weight of the ore charged of particle size of about 1 to about 10 mm. was required to produce the same effect on the sulphur content of the reduced pellets. The solid reductant had a particle size smaller than about 12 mm. and wasprovided in an amount suflicient to have in the discharge from the kiln at least 0.05 to 0.15 pound of carbon per pound of pellets charged to prevent re-oxidation at the discharge end of the kiln and to maintain reducing conditions in that area according to Reaction 4.

The most satisfactory and safe maximum temperature in the reduction zone of the kiln for the dilferent types of pellets are set out in Table 1 above.

There was no adherence of particles of the charge mixture to the wall of the reactor; there was substantially no agglomeration of the particles of the charge; there was an important saving in the cost of solid carbonaceous material by decreasing the amount of the excess carbon; the pellets were easily separated from the residual charge mixture; and the excess solid carbonaceous material discharged was maintained at a minimum.

A second set of pilot plant tests confirmed the above experimental results. The kiln employed in these pilot plant tests was feet long with an internal diameter of 7.5 feet and a slope of about 2 from the horizontal. Ten supplemental fuel burners, each having air conduits, were mounted on the kiln shell at 9 foot intervals and were offset radially in succession by 72. The kiln was rotated at 0.25 to 0.4 revolution per minute and processed the iron oxide pellets at charging rates of 80 to 200 net tons per day.

Indurated iron oxide pellets were within the size range of from about 6 mm. to about 15 mm. and averaged 66.7% by weight iron, 2% to 3% SiO 1% to 2% MgO and had a safe maximum temperature in the range of about 1100C. to about 1180C. A mixture of anthracite coals having 70.8% and 68.9% fixed carbon, 0.7% and 0.6% sulphur, and ash fusion temperatures of 1600C. and 1490C. respectively, were charged in the amount of 600 to 1200 pounds per ton of indurated iron oxide pellets in the feed yielding 0.08 to 0.28 pound of uncombusted carbon in the discharge product per pound of iron oxide pellets charged. Dolomite in the size range of from about 0.15 to about 6 mm. was charged from 0 to pounds per ton of iron oxide pellets charged. The kiln reaction temperature was maintained in the range of from about 1125C. to about 1200C. Natural gas, containing 88.1% methane, was supplied from about 1700 to about 2800 cubic feet per ton of iron oxide charged and air was supplied at a rate of from about 35,000 to about 55,000 cubic feet per ton of iron oxide pellets charged. On the basis of supplying 48,500 cubic feet of air per ton of iron oxide pellets charged for 2,200 cubic feet of natural gas per ton of iron oxide pellets charged, approximately 21,900 cubic feet of air were available for reaction with the natural gas and 23,700 cubic feet were available for reaction with the coal, the balance being discharged with the exhaust gas.

It was found that a sponge iron was produced having up to 97% of the iron in metallic state. The sulphur content was about 0.012% and the pellets were free of adhering flux and ash. The pellets of sponge iron ranged in size from 15 mm. to 0.8 mm. with about 2% smaller than 0.8 mm. As a specific illustration of the thermalefiiciency of the process, a product containing 95.2% iron in the metallic state required about 12.2 X 10 B.t.u. per ton of metallic iron, a considerably lower heat requirement than that required by known solid reduction processes operating on a commercial scale.

Green iron oxide pellets tested were within the size range of from about 3 mm. to about 15 mm. and averaged from about 57.5% to about 63%, by weight, iron and about 10%, by weight, moisture. Various sizes of anthracite coals in the size range of from about 0.15 mm. to about 6 mm. having from about 70.8 to about 68.9% fixed carbon, and 0.7% to about 0.6% sulphur, and ash fusion temperatures in the range of from about 1600C. to about 1490C., were charged in amount of about 900 to 2000 pounds per ton of green pellets in the feed, the preferred range being determined at from about 900 to up to 98.3% of the iron in metallic state.

13 about 1400 pounds, yielding from about 0.25 to 0.5 pound of uncombusted carbon in the discharge product per pound of green iron oxide pellets charged. The excessive quantity of solid carbonaceous material added was introduced to provide a cushion for the friable green pellets.

Dolomite in the size range of from 0.15 to about 6 mm. was charged from to 80 pounds per ton of iron oxide pellets charged. The kiln reaction temperature was maintained in the range of from about 1025 C. to about 1125 C. Natural gas, containing 88.1% methane was supplied from about 1900 to about 2850 cubic feet per ton of iron oxide pellets charged and air was supplied at a rate of from about 46,500 to about 56,300 cubic feet per ton of iron oxide pellets charged. On the basis of supplying 51,245 cubic feet of air per ton of green iron oxide pellets charged for 2,530 cubic feet of natural gas per ton of green iron oxide pellets charged, approximately 25,300 cubic feet of air were available for reaction with the natural gas and 24,300 cubic feet were available for reaction with the coal, the balance being discharged with the exhaust gas.

It was found that a sponge iron was produced having The sulphur content was about 0.06% and the pellets were free of adhering flux and ash.

The process of this invention possesses a number of important advantages. The operating temperature can be positively controlled throughout the heating, reducing and discharging zones to maintain optimum reducing conditions without agglomeration of particles of the charge mixture or adherence of particles to the wall of the reactor which would gradually restrict the useful volume of the reactor and necessitate frequent stoppages of the process for the purpose of cleaning. A significant reduction in the quantity of solid carbonaceous material required for the process is effected resulting in important savings in the cost of solid carbonaceous matter required for the process and an increased kiln capacity. It is possible to control the rate and degree of reduction to a desired level to produce, efficiently and economically, a metallic iron-iron oxide product which is suitable for charging into either iron or steel making furnaces.

What we claim as new and desire to protect by Letters Patent of the United States is:

1. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mixture of iron oxide of a particle size within the range of from about 3 mm. to about mm., solid carbonaceous material of a particle size of from about 0.15 mm. to about 12 mm., and a flux in which the major portion is of a particle size larger than about 0.5 mm., the carbonaceous material being supplied in an amount which provides from about 50% to about 90% of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture;

(b) advancing the charge mixture to the reduction zone and reacting the charge mixture therein at a temperature within the range of from about 650 C. to about 1200 C. but below the agglomeration temperature of the charge mixture;

(c) maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length, combustible material which provides from about 50% to about 10% of the total fuel energy which is required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which per- 14 mits the discharge of carbon with the reacted charge mixture; and

(d) adding a free oxygen containing gas at spaced intervals along its length in amount sufficient to provide oxygen for reaction with the supplemental fuel and a portion of the solid carbonaceous material to supply the necessary heat and reducing gases.

2. The process according to claimv 1 in which the supplemental fuel and free oxygen bearing gas are added in a direction substantially parallel to the axis of the kiln concurrent with the flow of the charge mixture.

3. The process according to claim 1 in which the supplemental fuel and free oxygen bearing gas are added in a direction substantially parallel to the axis of the kiln countercurrent to the flow of the charge mixture.

4. The process according to claim 1 in which the supplemental fuel and freeoxygen bearing gas are added in a direction substantially parallel to the axis of the kiln concurrent with and countercu-rrent to the flow of the charge mixture.

5. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mixture of iron oxide of a particle size within the range of from about 3 mm. to about 15 mm., solid carbonaceous material of a particle size larger than 0.15 mm., and a flux of a particle size in which the major portion is in the size range of from about 0.5 mm. to about 3 mm., the carbonaceous material being supplied in an amount which provides from about 50% to about of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture;

(b) advancing the charge mixture to the reduction zone and reacting the charge mixture therein at a temperature within the range of from about 650 C. to about 1200 C. but below the agglomeration temperature of the charge mixture;

(0) maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length in a direction substantially parallel to the axis of the kiln, combustible material selected from the group consisting of particulated solid, liquid and gaseous carbon-containing materials which provides from about 50% to about 10% of the total fuel energy which is required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of carbon with the reacted charge mixture;

(d) adding a free oxygen containing gas at spaced intervals along its length in a direction substantially parallel to the axis of the kiln in amount sufficient to provide oxygen for reaction with the supplemental fuel and solid carbonaceous material to supply the necessary heat and reducing gases; and

(e) maintaining throughout the reduction zone a partial pressure of carbon monoxide sufficient to drive the reaction in the direction of the formation of metallic iron.

6. In a process as claimed in claim 5, said iron oxide being in the form of indurated pellets.

7. In a process as claimed in claim 5, said iron oxide being in the form of green pellets.

8. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mixture of iron oxide of a particle size within the range of from about 3 mm. to about 15 mm., solid carbonaceous material of a particle size of from about 0.15 mm. to about 12 mm., and a flux in which the major portion is of a particle size within the range of from about 0.5 mm. to about 3 mm., the carbon content of the carbonaceous material being provided in an amount which provides from about 50% to about 90% of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge with the reacted charge mixture of from about 0.05 pound to about 0.5 pound of carbon per pound of iron oxide in the feed;

(b) advancing the charge mixture to the reduction zone and reacting it therein with reducing gas flowing countercurrent to the charge mixture at a temperature within the range of from about 650 C. to about 1200" C., but below the agglomerating temperature of the charge mixture;

() maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length in a direction substantially parallel to the axis of the kiln, combustible material selected from the group consisting of particulated solid, liquid and gaseous carbon-containing materials which provides from about 50% to about of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge with the reacted charge mixture of from about 0.05 pound to about 05 pound of carbon per pound of iron oxide in the feed;

(d) adding a free oxygen containing gas at spaced intervals along its length in a direction substantially parallel to the axis of the kiln in amount sufficient to provide oxygen for reaction with substantially all the supplemental fuel and at least 20% of the solid carbonaceous material to supply the necessary heat and reducing gases; and

(e) maintaining throughout the reduction zone a partial pressure of carbon monoxide sufiicient to drive the reaction in the direction of the formation of metallic iron.

9. In a process as claimed in claim 8, said iron oxide being in the form of indurated pellets.

10. In a process as claimed in claim 8, said iron oxide being in the form of green pellets.

11. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mixture of iron oxide of a particle size within the range of from about 3 mm. to about mm., solid carbonaceous material of a particle size of from about 0.15 to about 12 mm., and a flux in which the major portion is of a particle size within the range of from about 0.5 to about 3 mm., the carbon content of the carbonaceous material being provided in an amount which provides from about 50% to about 90% of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge with the reacted charge mixture of from about 0.05 pound to about 0.5 pound of carbon per pound of iron oxide in the feed;

(b) advancing the charge mixture to the reduction zone and reacting it therein with reducing gas fiowing countercurrent to the charge mixture at a temperature within the range of from about 650 C. to about 1200 C., but below the agglomerating temperature of the charge mixture;

(c) maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length in a direction substantially parallel to the axis of the kiln, combustible material selected from the group consisting of particulated solid, liquid and gaseous carbon-containing materials which provides from about 50% to about 10% of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge with the reacted charge mixture of from about 0.05 pound to about 0.5 pound of carbon per pound of iron oxide in the feed;

(d) adding a free oxygen containing gas at spaced intervals along its length in a direction substantially parallel to the axis of the kiln in amount sufficient to provide oxygen for reaction with substantially all the supplemental fuel and at least 20% of the solid carbonaceous material to supply the necessary heat and reducing gases;

(e) maintaining throughout the reduction zone a partial pressure of carbon monoxide sufficient to drive the reaction in the direction of the formation of metallic iron;

(f) advancing the charge mixture through the reduction zone to the discharging zone countercurrent to the flow of hot reducing gases;

(g) discharging reacted charge mixture from the discharging zone and cooling said reacted charge mixture in a reducing or neutral atmosphere;

(h) separating metallic constituents of said reacted charge mixture from non-metallic constituents; and

(i) separating and re-cycling solid carbon within the size range of from about 0.15 mm. to about 12 mm. to the reduction zone in an amount of 0.05 pound to 0.5 pound per pound of iron oxide in the feed.

12. In a process as claimed in claim 11, said iron oxide being in the form of indurated pellets.

13. In a process as claimed in claim 11, said iron oxide being in the form of green pellets.

14. The process according to claim 11 in which the supplemental fuel and free oxygen bearing gas are added in a direction substantially parallel to the axis of the kiln concurrent with the flow of the charge mixture.

15. The process according to claim 11 in which the supplemental fuel and free oxygen bearing gas are added in a direction substantially parallel to the axis of the kiln countercurrent to the flow of the charge mixture.

16. The process according to claim 11 in which the supplemental fuel and free oxygen bearing gas are added in a direction substantially parallel to the axis of the kiln concurrent with and countercurrent to the fiow of the charge mixture.

17. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mixture of indurated iron oxide pellets of a particle size within the range of from about 6 mm. to about 15 mm., solid carbonaceous material of a particle size of from about 1 mm. to about 12 mm., and a flux of limestone or dolomite substantially in the size range of from about 0.5 mm. to about 3 mm., the carbon content of the solid carbonaceous material being supplied in an amount less than about 150% of the amount theoretically required for reduction of the iron oxide pellets in the charge which provides from about 50% to about of the total fuel energy required for reduction of the iron content of the charge and maintaining the kiln at the desired reaction temperature, and which permits the discharge of the carbon with the reacted charge mixture;

(b) advancing the charge mixture to the reduction zone and reacting it therein with reducing gas flowing countercurrent to the charge mixture at a temperature within the range of from about 650 C.

17 18 to about 1200 C., but below the agglomerating rtion zone to the discharging zone countercurrent temperature of the charge mixture; to the flow of hot reducing gases;

() maintaining the reduction zone at a substantially (g) discharging the reacted charge mixture from the uniform temperature throughout its length by supdischarging zone and cooling said reacted charge plying from an external source, at spaced intervals mixture in a reducing or neutral atmosphere; along its length, combustible material which pro- (h) separating metallic constituents of said reacted vides from about 50% to about of the total charge mixture from non-metallic constituents; and fuel energy required for reduction of the iron con- (i) separating and re-cycling solid carbon within the tent of the charge and maintaining the kiln at the size range of from about 0.15 mm. to about 6 mm. desired reaction temperature, and which permits 10 19. A process for the reduction of iron oxide in a rothe discharge of carbon with the reacted charge tary kiln-type reactor having a heating zone, a reducing mixture; zone and a discharging zone which comprise the steps of:

(d) adding a free oxygen containing gas at spaced (a) feeding into the heating zone of the kiln a mixture intervals along its length in amount suflicient to of iron oxide of a particle size within the range of provide oxygen for reaction with substantially all from about 3 mm. to about 15 mm., solid carbonathe supplemental fuel and :at least of the solid ceous material of a particle size larger than 0.15 carbonaceous material to supply the necessary heat mm., and a flux of a particle size in which the major and reducing gases; portion is in the size-range of from about 0:5 mm. to

( maintaining throughout the reduction e a Parabout 3 mm., the carbonaceous material being protial pressure of carbon monoxide sufiicient to drive 20 id d i an a o t hi h provides from about 60% the reaction in the direction of the formation of t abo t 80% of th total fuel energy required for metallic reduction of the iron content of the charge and mainadvancing the Charge IniXtuTe through the reduotaining the kiln at the desired reaction temperature, tion zone to the discharging zone countercurrent to d hi h permits th discharge of carbon with the the flow of hot reducing gases; reacted charge i t (g) discharging the reacted Charge 'e from the (b) advancing the charge mixture to the reduction discharging Zone and Cooling Said reacted charge zone and reacting the charge mixture therein at a mixture in a reducing or neutral p temperature within the range of from about 650 C.

(h) separating metallic constituents of said reacted to about 12()() C b b l the agglomeration charge mixture from non-metallic constituents; and perature of h charge i (i) separating and re-cycling solid carbon within the size range of from about 1 mm. to about 12 mm. to the reduction zone.

18. A process for the reduction of iron oxide in a rotary kiln-type reactor having a heating zone, a reducing zone and a discharging zone which comprises the steps of:

(a) feeding into the heating zone of the kiln a mix- (c) maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length in a direction substantially parallel to the axis of the kiln, combustible material selected from the group consisting of particulated solid, liquid and gaseous carbon-containing materials in an amount tuIe of green iron oXide pellets of a Partiele Size which provides from about to about 20% of Within the range of from about 3 to about 15 the total fuel energy which is required for reduction Solid carbonaceous material of 3 Particle Size of 40 of the iron content of the charge and maintaining the from about to about 6 and a flux of kiln at the desired reaction temperature, and which limestone or dolomite substantially in the size range permits h di h of carbon i h h reacted of from about 0.5 mm. to about 3 mm., the solid charge i carbonaceous material bfilllg supplied in an amount adding a free Oxygen containing gas at paced in- Which Provides from about 50% to about 90% of tervals along its length in a direction substantially the total fuel energy theoretically required for redueparallel to the axis of the kiln in amount suflicient tion of the iron oxide Pellets in the Charge together to provide oxygen for reaction with the supplemental with sufiicient carbonaceous material to provide in f l d bo t 20% to about 75% of th olid arbothe reacted Product to Pound of Carbon P naceous material to supply the necessary heat and repound of iron oxide pellets charged; ducing gases; and

(b) advancing the charge mixture to the redu t n (e) maintaining throughout the reduction zone a par- Zone and reacting it therein With reducing g flowing tial pressure of carbon monoxide suflicient to drive countercurrent 0 the h g mixture at a p the reaction in the direction of the formation of ture within the range of from about 650 C. to about metallic iron, 1200 C., but below the agglomerating temperature 20. In a process as claimed in claim -19, said iron oxide of the charge mixture; being in the form of indurated pellets.

(c) maintaining the reduction zone at a substantially 21. In a process as claimed in claim 19, said iron oxide uniform temperature throughout its length by supbeing in the form of green pellets. plying from an external source, at spaced intervals 22. A process for the reduction of iron oxide in a rotary along its length, combustible material which prokiln-type reactor having a heating zone, a reducing zone vides from about 10% to about 50% of the total fuel and a discharging zone which comprises the steps of: energy required for reduction of the iron C nt nt f (a) feeding into the heating zone of the kiln a mixture the charge and for maintaining the kiln at the desired of iron oxide pellets of a particle size within the reaction temperature; range of from about 3 mm. to about 15 mm., solid (d) adding a free oxygen containing gas at spaced in- 5 carbonaceous material of a particle size of from tervals along its length in amount sufiicient to proabout 0.15 to about 12 mm., and a flux in which the vide oxygen for reaction with substantially all the major portion is of a particle size within the range supplemental fuel and at least 20% of the solid carof from about 0.5 to about 3 mm., the carbon conbonaceous material to supply the necessary heat and tent of the carbonaceous material being provided in reducing gases; an amount which provides from about 60% to about (e) maintaining throughout the reduction zone a par- 80% of the total fuel energy required for reduction tial pressure of carbon monoxide sufficient to drive of the iron content of the charge and maintaining the reaction in the direction of the formation of the kiln at the desired reaction temperature, and metallic iron; which permits the discharge with the reacted charge (f) advancing the charge mixture through the reducmixture of from about 0.08 pound to about 0.5 pound 19 20 of carbon per pound of iron oxide pellets in the feed; tial pressure of carbon monoxide suflicient to drive (b) advancing the charge mixture to the reduction zone the IBaCtiOn in th directi n Of the formation of and reacting it therein with reducing gas flowing metallic iron; countercurrent to the charge mixture at a temperaadvancing the charge fi through the reducture within the range of from about to about Hon zone to the discharging zone countercurrent to the fiow of hot reducing gases;

(g) discharging reacted charge mixture from the discharging zone and cooling said reacted charge mixture in a reducing or neutral atmosphere;

(h) separating metallic constituents of said reacted charge mixture from non-metallic constituents; and

(i) separating and re-cycling solid carbon within the 1200 C., but below the agglomerating temperature of the charge mixture;

(0) maintaining the reduction zone at a substantially uniform temperature throughout its length by supplying from an external source, at spaced intervals along its length in a direction substantially parallel to the axis of the kiln, combustible material selected Size range f f o about 015 to about 12 mm from the group Consisting of Particulated Solid, quid to the reduction zone in an amount of 0.08 pound and gaseous carbon-containing materials which proto 0.5 pound per pound of iron oxide pellets in the vides from about to about of the total fuel feed.

energy required for reduction of the iron content of the charge and maintaining the kiln at the desired References Cited by the Examiner reaction temperature, and which permits the dis- UNITED STATES PATENTS charge with the reacted charge mixture of from about 20 890,234 6/1808 Jones 4 0.08 pound to about 0.5 pound of carbon per pound ,7 9 9 2 19 0 Hornsey 75 of iron oxide pellets in the feed; 2,434,911 1 1949 s n 75 5 (d) adding a free oxygen containing gas at spaced in- 2,593,398 4/ 1952 Kalling 75 3 tervals along its length in a direction substantially 2,754,197 7/1956 Wienert 75-36 parallel to the axis of the kiln in amount sufficient to 20 2,829,042 4/ 1958 Moklebust 75-36 provide oxygen for reaction with substantially all the 2,855,290 10/ 8 Freeman 75--33 supplemental fuel and about 20% to about 75% of ,877,108 3/1959 Smith 7536 the solid carbonaceous material to supply the neces- 2,941,791 6/1960 Wienfift 7534 sary heat and reducing gases; 30 3,029,141 4/1962 Sibakin 7534 (e) maintaining throughout the reduction zone a par- DA L RECK, Primary Examiner 

1. A PROCESS FOR THE REDUCTION OF IRON OXIDE IN A ROTARY KILN-TYPE REACTOR HAVING A HEATING ZONE, A REDUCING ZONE AND A DISCHARGING ZONE WHICH COMPRISES THE STEPS OF: (A) FEEDING INTO THE HEATING ZONE OF THE KILN A MIXTURE OF IRON OXIDE OF A PARTICLE SIZE WITHIN THE RANGE OF FROM ABOUT 3 MM. TO ABOUT 15 MM., SOLID CARBONACEOUS MATERIAL OF A PARTICLE SIZE OF FROM ABOUT 0.15 MM. TO ABOUT 12 MM., AND A FLUX IN WHICH THE MAJOR PORTION IS OF A PARTICLE SIZE LARGER THAN ABOUT 0.5 MM., THE CARBONACEOUS MATERIAL BEING SUPPLIED IN AN AMOUNT WHICH PROVIDES FROM ABOUT 50% TO ABOUT 90% OF THE TOTAL FUEL ENERGY REQUIRED FOR REDUCTION OF THE IRON CONTENT OF THE CHARGE AND MAINTAINING THE KILN AT THE DESIRED REACTION TEMPERATURE, AND WHICH PERMITS THE DISCHARGE OF CARBON WITH THE REACTED CHARGE MIXTURE; (B) ADVANCING THE CHARGE MIXTURE TO THE REDUCTION ZONE AND REACTING THE CHARGE MIXTURE THEREIN AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 650*C. TO ABOUT 1200*C. BUT BELOW THE AGGLOMERATION TEMPERATURE OF THE CHARGE MIXTURE; (C) MAINTAINING THE REDUCTION ZONE AT A SUBSTANTIALLY UNIFORM TEMPERATURE THROUGHOUT ITS LENGTH BY SUPPLYING FROM AN EXTERNAL SOURCE, AT SPACED INTERVALS ALONG ITS LENGTH, COMBUSTIBLE MATERIAL WHICH PROVIDES FROM ABOUT 50% TO ABOUT 10% OF THE TOTAL FUEL ENERGY WHICH IS REQUIRED FOR REDUCTION OF THE IRON CONTENT OF THE CHARGE AND MAINTAINING THE KILN AT THE DESIRED REACTION TEMPERATURE, AND WHICH PERMITS THE DISCHARGE WITH THE REACTED CHARGE MIXTURE; AND (D) ADDING A FREE OXYGEN CONTAINING GAS AT SPACED INTERVALS ALONG ITS LENGTH IN AMOUNT SUFFICIENT TO PROVIDE OXYGEN FOR REACTION WITH THE SUPPLEMENTAL FUEL AND A PORTION OF THE SOLID CARBONACEOUS MATERIAL TO SUPPLY THE NECESSARY HEAT AND REDUCING GASES. 